Method for recovering precious metal

Abstract

A method for recovering precious metal from an acidic aqueous solution containing dissolved precious metal and free chlorine, comprising the following successive steps: (1) combining a salt of a non-precious metal present in a low oxidation state as a solid or as an aqueous solution with the acidic aqueous solution to consume the free chlorine and form an acidic aqueous mixture, and (2) adding non-precious metal to the acidic aqueous mixture formed in step (1) to precipitate elementary precious metal.

The invention claimed is: 
     
       1. A method for recovering precious metal from an acidic aqueous solution containing dissolved precious metal and free chlorine, the method comprising the following successive steps:
 (1) providing an acidic aqueous solution containing precious metal and free chlorine; 
 (2) combining a salt of a non-precious metal present in a low oxidation state as a solid or as an aqueous solution with the acidic aqueous solution to completely or substantially completely consume the free chlorine and form an acidic aqueous mixture, and 
 (3) adding non-precious metal to the acidic aqueous mixture formed in step (2) to precipitate elementary precious metal, wherein 
 the acidic aqueous solution is characterized by (i) a fraction of dissolved precious metal in the range of 100 to 500 mg/l, (ii) a pH in the range of −0.8 to +1 and (iii) a content of the free chlorine in the range of 0.1 to 1 g/l, and 
 the dissolved precious metal comprises at least one precious metal selected from the group consisting of gold, platinum, palladium, rhodium, iridium, osmium and ruthenium. 
 
     
     
       2. The method according to  claim 1 , wherein the acidic aqueous solution is a mother liquor originating from wet chemical precious metal recycling or wet chemical precious metal refining. 
     
     
       3. The method according to  claim 1 , wherein the acidic aqueous solution further comprises hydrochloric acid. 
     
     
       4. The method according to  claim 1 , wherein the salt used in step (2) comprises one or more salts selected from tin (II) salts, iron (II) salts, and combinations thereof. 
     
     
       5. The method according to  claim 1 , wherein the salt used in step (2) is used in a stoichiometric or superstoichiometric amount in relation to free chlorine to be consumed. 
     
     
       6. The method according to  claim 1 , wherein the non-precious metal used in step (3) is selected from zinc, iron and combinations of zinc and iron. 
     
     
       7. The method according to  claim 1 , wherein the non-precious metal used in step (3) is added in a superstoichiometric amount in relation to precious metal present in dissolved form and to be precipitated in elemental form. 
     
     
       8. The method according to  claim 6 , wherein the non-precious metal used in step (3) is in the form of a powder. 
     
     
       9. A method for recovering precious metal from an acidic aqueous solution containing dissolved precious metal and free chlorine, the method comprising the following successive steps:
 (1) providing an acidic aqueous solution containing precious metal and free chlorine; 
 (2) combining a salt of a non-precious metal present in a low oxidation state as a solid or as an aqueous solution with the acidic aqueous solution to completely or substantially completely consume the free chlorine and form an acidic aqueous mixture, and 
 (3) adding non-precious metal to the acidic aqueous mixture formed in step (2) to precipitate elementary precious metal, wherein 
 the acidic aqueous solution is characterized by (i) a fraction of dissolved precious metal in the range of 100 to 500 mg/l, (ii) a pH in the range of −0.8 to +1 and (iii) a content of free chlorine in the range of 1000 to 10,000 ppm by weight, and 
 the dissolved precious metal comprises at least one precious metal selected from the group consisting of gold, platinum, palladium, rhodium, iridium, osmium and ruthenium. 
 
     
     
       10. The method according to  claim 9 , wherein the acidic aqueous solution is a mother liquor originating from wet chemical precious metal recycling or wet chemical precious metal refining. 
     
     
       11. The method according to  claim 9 , wherein the pH of the acidic aqueous solution is in the range of −0.8 to less than −0.5. 
     
     
       12. The method according to  claim 9 , wherein the acidic aqueous solution further comprises hydrochloric acid. 
     
     
       13. The method according to  claim 9 , wherein the salt used in step (2) comprises one or more salts selected from tin (II) salts, iron (II) salts, and combinations thereof. 
     
     
       14. The method according to  claim 9 , wherein the salt used in step (2) is used in a stoichiometric or superstoichiometric amount in relation to free chlorine to be consumed. 
     
     
       15. The method according to  claim 9 , wherein the non-precious metal used in step (3) is selected from zinc, iron and combinations of zinc and iron. 
     
     
       16. The method according to  claim 15 , wherein the non-precious metal used in step (3) is in the form of a powder. 
     
     
       17. The method according to  claim 9 , wherein the non-precious metal used in step (3) is added in a superstoichiometric amount in relation to precious metal present in dissolved form and to be precipitated in elemental form.